One solution to solid waste disposal has been to place the solid waste (including MSW) into landfills. Other solutions to the disposal problem included mass incineration, preparation and combustion of refuse derived fuel (RDF), and size reduction for composting. Each of these methods have undesirable consequences. For example, most of the waste (excluding plastics, metals and glass) becomes lost and are, therefore, not recyclable. Plastics, metals and glass, while not lost, become nearly permanent components of the disposal site due to the chemical resistance and non-biodegradable nature of these polymers. In the combustion of plastics, hydrocarbons, dioxins, furans, acid gases and NOx, emissions in the stack gases of mass burn or RDF incineration facilities can be major sources of air pollution with rather severe health and environmental consequences unless severe, expensive pollution control measures are in place.
In my prior U.S. Pat. No. 4,342,830, dated Aug. 3, 1982, steam treatment of MSW is disclosed wherein the sterilized and softened organics are forced through perforations upon sudden release of pressure whereby inorganics and certain synthetics, such as metal cans, glass, and the like are left behind. This method included the addition of significant quantities of water to the wastes and thus required substantial energy consumption in the form of steam to heat the water/waste slurry and to force the resultant sterile and softened organics through the perforations in a singular step. The plastics recovered which were suitable for recycling were generally less than 2% of the waste by weight and were generally severely contaminated with softened organics and dirt. The inorganic materials such as ferrous and non-ferrous metals were also similarly contaminated making these products less desirable for recycling. The glass components were both broken and contaminated.
In my prior U.S. Pat. No. 4,540,495, dated 10, 1985, steam treatment was again disclosed wherein the amount of water added prior to steam treatment was significantly reduced to conserve the energy consumed and to reduce the moisture content of the softened organic fraction to in the order of 60% by weight. The internal steam pressure requirements in combination with the resultant temperatures and the necessary period of time it took to cook and sterilize the waste material and soften the organic matter also caused a melting of many plastics and significant heat distortion of most other plastics as in the previous U.S. Pat. No. 4,342,830.
Also, in my prior U.S. Pat. No. 4,844,351 a method for separation, recovery and recycling of plastics from municipal solid waste was disclosed wherein mixed wastes including various plastic elements were subjected to mechanical agitation and heat distortion. The wastes were introduced into a processing unit having a means for heating and a means for agitating the wastes. By this method, the plastics were separated and recovered as a mixture that may be recycled. The processing unit included an inclined, cylindrical rotatable vessel having closure members (hatches) at opposite ends thereof. A plurality of spaced plates, inclined in a common plane and secured to the internal wall of the cylinder extends into the interior of the cylinder. The plates were arranged to only provide a lifting and mixing action to the waste material; however, because of the arrangement of the plastic, only a small degree of mixing of the materials could be accomplished.
The above noted defects of the prior art is overcome by the method and structure of the present invention which provides for "extruding" the waste materials in a pressurized heated container. Such extrusion process provides for substantially "fluidizing" the organic material thus making it more easily separated from the inorganic materials such as glass, metals, etc.